The nicotinic acetylcholine receptor couples neuromuscular transmission by increasing Na ion and K ion conductance in response to pre-synaptic release of acetylcholine. The AChR has recently been purified from the electric organs of electric eel and electric ray, which are rich sources of this important protein. This advance has been possible largely because of the availability of certain snake neurotoxins which specifically bind the AChR. These neurotoxins, when radio-labelled, provide the basis for an assay and can also serve as affinity ligands in the purification of AChR. It has become clear that the electric fish AChR in many ways closely resembles mammalian muscle. However, comparison must await characterization of AChR from mammalian muscle, an inherently more difficult problem because of the low levels of AChR present. We have recently been able to purify the AChR from both normal and denervated skeletal muscle. It is the initial objective of this proposal to achieve large scale purification of the AChR from these sources. The purified AChR will then be subjected to extensive biochemical and pharmacological characterization. A number of differences have been reported between synaptic and extrajunctional AChR, including drug sensitivities, rates of degradation, conductance parameters and immunological reactivity. These studies should reveal the biochemical basis for such differences. The disease Myasthenia Gravis is thought to involve an autoimmune component, and patients in acute myasthenic trauma have antibodies directed against the AChR. We will routinely monitor the levels of anti-AChR IgG in the sera of myasthenic patients.